1. Field of the Invention
The invention relates to a method and system or apparatus for removing insoluble particles of mercury containing amalgam and other metals and soluble and suspended mercury from a dental waste slurry.
2. Description of the Prior Art
Dental amalgam is a common dental restorative material which contains silver, zinc, copper, tin and mercury, and occasionally other metals. During the most commonly performed dental procedures, dental amalgam containing mercury is removed as waste material from the patient's mouth. Removal of the amalgam typically takes place by vacuum extraction as part of a rinsing liquid, such as water. The mercury removed is in the form of mercury-containing particulate matter and the soluble and suspended mercury-containing fraction. Other material such as saliva, blood, pieces of dental appliances, etc. are also removed to form a liquid waste water slurry.
Mercury is generally classified as a toxic material which requires special handling and disposal procedures. Since the removed dental amalgam contains mercury, a need exists to separate the mercury-containing particulate matter and the soluble and suspended mercury-containing fraction from the waste water slurry extracted from the patient's mouth prior to eventual discharge of the waste water into the public sewer system. After removal from the waste water slurry, the mercury-containing waste can then be disposed of or reclaimed.
Apparatus previously has been disclosed, such as in U.S. Pat. Nos. 3,777,403 to Ritchie and 4,385,891 to Ligotti which use different containers through which the mixture of liquid and solids are passed and the solids settle out under the force of gravity. While such is apparatus may be satisfactory for the collection of large particles from a dental waste stream slurry mixture, they are not specifically designed to sediment, and later remove, all mercury-containing particulate matter and allow treatment of soluble and suspended mercury in the waste stream. In these patents, soluble material does not settle out by force of gravity. Instead, it is entrained in the liquid stream which is usually treated like waste water and disposed of in a commercial drain system. This is not satisfactory since the contaminated liquid waste may cause eventual contamination of the water supply and violate local sanitary district regulations, or those of other agencies, for mercury levels in waste water. Also, the systems of these patents do not provide for treatment or removal of the mercury remaining in the supernatant after the settling of particles by gravity is completed.
Ludviggson et al. U.S. Pat. No. 5,205,743 discloses a system in which the waste material is collected in a suction stream and passed through filters. This does not provide for collection of liquid waste mixture expelled by a patient into a collection sink or collection and disposal of any soluble mercury. Bishop U.S. Pat. No. 3,138,873 uses a suction system which passes a liquid slurry of the waste material through a porous bag which traps and collects the solid particles and passes the liquid. This apparatus must have a compromise as to the size of the particles collected and the liquid flow rate as determined by the porosity of the bag. Also, it makes no provision to collect soluble mercury.
In Meyer U.S. Pat. No. 5,017,135, particles are separated from the waste liquid as it is drawn under suction force in a sharply turning path past a series of traps into which particles settle out under force of gravity. Here also, no specific provision is made for collection of small particles or soluble mercury. Sundstrom U.S. Pat. No. 5,114,578 passes a slurry of water, saliva and particles through a pre-settling tank, into which the larger particles settle, and then in an upward inclined path through a special filter formed by a bundle of plastic tubes. In using this arrangement it is difficult to collect and dispose of the smaller metal particles collected on the walls of the filter and filter plastic tubes and there is no provision for the treatment of the soluble mercury.